People with blood cancers like leukaemia have to undergo chemotherapy to eradicate the blood cells that are causing their cancer. The collateral damage is that most, if not all their healthy blood cells go too. Stem cells from bone marrow transplants are used to repopulate their circulatory system with healthy blood cells. The transplant has an extra benefit: the new immune cells in the blood can help finish off any residual cancer cells that survived the chemotherapy.
Increasingly, donated umbilical cord blood – which contains fetal stem cells – is being used instead of bone marrow transplants because the risk of rejection is lower with the immature cells. But doctors thought this came at a price – if the immune cells in the cord blood are less aggressive to the recipient, then presumably they are also less aggressive to any residual leukaemia cells.
Not so naive after all
Now, an experiment in mice has shown the exact opposite. “We thought the baby cells were much tamer,” says team member Paul Veys of Great Ormond Street Hospital for Children in London. “The assumption has been that they won’t fight but it’s the complete reverse,” he says.
Veys and his colleagues compared the impact of injecting immune cells from adult or cord blood into mice with a form of human blood cancer called B-cell lymphoma. Tumours rapidly disappeared in the mice that received the fetal immune cells, but kept growing in those that got the adult cells.
When the researchers examined tumour samples from the animals before they were destroyed, they found that the fetal cells triggered rapid production of CD4 cells, the white blood cells that orchestrate the immune system response to tumours and viruses. Moreover, the tumours rapidly filled up with CD8 cells, the killer cells that actually destroy cancerous tissue.
The result was a surprise because the assumption has always been that compared with “seasoned” adult cells, the immune cells in the cord blood would be too naive to recognise and kill abnormal cells. “Instead, it seems they can pitch straight in without practice,” says Veys. He speculates that the cells may have special immunological abilities that provide immediate protection to a growing fetus. “The implication is that using cord blood may be a better choice to mop up leukaemia,” he says.
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